Fix TypeError: 'NoneType' object is not iterable

[sbrunner]

Traceback (most recent call last):
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 137, in run
    self.result = application(self.environ, self.start_response)
  File "/usr/local/lib/python3.10/dist-packages/prometheus_client/exposition.py", line 129, in prometheus_app
    status, headers, output = _bake_output(registry, accept_header, accept_encoding_header, params, disable_compression)
  File "/usr/local/lib/python3.10/dist-packages/prometheus_client/exposition.py", line 105, in _bake_output
    output = encoder(registry)
  File "/usr/local/lib/python3.10/dist-packages/prometheus_client/openmetrics/exposition.py", line 21, in generate_latest
    for metric in registry.collect():
  File "/usr/local/lib/python3.10/dist-packages/prometheus_client/registry.py", line 97, in collect
    yield from collector.collect()
  File "/usr/local/lib/python3.10/dist-packages/c2cwsgiutils/prometheus.py", line 135, in _deserialize_collected_data
    for serialized_metric in serialized_collection:
TypeError: 'NoneType' object is not iterable
----------------------------------------
Exception occurred during processing of request from ('10.10.38.202', 55654) Traceback (most recent call last):
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 137, in run
    self.result = application(self.environ, self.start_response)
  File "/usr/local/lib/python3.10/dist-packages/prometheus_client/exposition.py", line 129, in prometheus_app
    status, headers, output = _bake_output(registry, accept_header, accept_encoding_header, params, disable_compression)
  File "/usr/local/lib/python3.10/dist-packages/prometheus_client/exposition.py", line 105, in _bake_output
    output = encoder(registry)
  File "/usr/local/lib/python3.10/dist-packages/prometheus_client/openmetrics/exposition.py", line 21, in generate_latest
    for metric in registry.collect():
  File "/usr/local/lib/python3.10/dist-packages/prometheus_client/registry.py", line 97, in collect
    yield from collector.collect()
  File "/usr/local/lib/python3.10/dist-packages/c2cwsgiutils/prometheus.py", line 135, in _deserialize_collected_data
    for serialized_metric in serialized_collection:
TypeError: 'NoneType' object is not iterable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.10/socketserver.py", line 683, in process_request_thread
    self.finish_request(request, client_address)
  File "/usr/lib/python3.10/socketserver.py", line 360, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python3.10/socketserver.py", line 747, in __init__
    self.handle()
  File "/usr/lib/python3.10/wsgiref/simple_server.py", line 134, in handle
    handler.run(self.server.get_app())
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 145, in run
    self.handle_error()
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 382, in handle_error
    self.finish_response()
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 184, in finish_response
    self.write(data)
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 288, in write
    self.send_headers()
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 346, in send_headers
    self.send_preamble()
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 268, in send_preamble
    self._write(
  File "/usr/lib/python3.10/wsgiref/handlers.py", line 467, in _write
    result = self.stdout.write(data)
  File "/usr/lib/python3.10/socketserver.py", line 826, in write
    self._sock.sendall(b)
BrokenPipeError: [Errno 32] Broken pipe
----------------------------------------
HTTP/1.1 10.10.37.248:8080 GET /config/c2c/health_check? "-" "kube-probe/1.27" 200 30 2295 <9> HTTP/1.1 10.10.37.248:8080 GET /config/c2c/health_check? "-" "kube-probe/1.27" 200 30 2461 <9>

and

06:02:03.509568 W c2cwsgiutils.redis_utils Redis connection problem
Traceback (most recent call last):

  File "/usr/local/lib/python3.10/dist-packages/c2cwsgiutils/redis_utils.py", line 115, in run
    pubsub.get_message(ignore_subscribe_messages=True, timeout=1)

  File "/usr/local/lib/python3.10/dist-packages/redis/client.py", line 1013, in get_message
    response = self.parse_response(block=(timeout is None), timeout=timeout)

  File "/usr/local/lib/python3.10/dist-packages/redis/client.py", line 824, in parse_response
    response = self._execute(conn, try_read)

  File "/usr/local/lib/python3.10/dist-packages/redis/client.py", line 800, in _execute
    return conn.retry.call_with_retry(

  File "/usr/local/lib/python3.10/dist-packages/redis/retry.py", line 49, in call_with_retry
    fail(error)

  File "/usr/local/lib/python3.10/dist-packages/redis/client.py", line 802, in <lambda>
    lambda error: self._disconnect_raise_connect(conn, error),

  File "/usr/local/lib/python3.10/dist-packages/redis/client.py", line 789, in _disconnect_raise_connect
    raise error

  File "/usr/local/lib/python3.10/dist-packages/redis/retry.py", line 46, in call_with_retry
    return do()

  File "/usr/local/lib/python3.10/dist-packages/redis/client.py", line 801, in <lambda>
    lambda: command(*args, **kwargs),

  File "/usr/local/lib/python3.10/dist-packages/redis/client.py", line 818, in try_read
    if not conn.can_read(timeout=timeout):

  File "/usr/local/lib/python3.10/dist-packages/redis/connection.py", line 478, in can_read
    return self._parser.can_read(timeout)

  File "/usr/local/lib/python3.10/dist-packages/redis/_parsers/base.py", line 128, in can_read
    return self._buffer and self._buffer.can_read(timeout)

  File "/usr/local/lib/python3.10/dist-packages/redis/_parsers/socket.py", line 95, in can_read
    return bool(self.unread_bytes()) or self._read_from_socket(

  File "/usr/local/lib/python3.10/dist-packages/redis/_parsers/socket.py", line 68, in _read_from_socket
    raise ConnectionError(SERVER_CLOSED_CONNECTION_ERROR)

redis.exceptions.ConnectionError: Connection closed by server.

06:02:04.042653 I c2cwsgiutils.redis_utils Redis is back